Glazing panel

ABSTRACT

A glazing panel carrying a solar control coating stack comprising in sequence at least: a glass substrate base antireflective layer comprising at least one layer comprising a nitride of aluminium an infra-red reflecting layer; and a top antireflective layer. The nitride of aluminium confers, inter alia, good thermal stability on the coating, particularly during heat treatment.

This application is a Continuation-in-part (CIP) of application Ser. No. 09/466,785 Filed on Dec. 20,1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to glazing panels and particularly, but not exclusively, to solar control glazing panels which are intended to undergo heat treatment following application of a solar control filter.

2. Discussion of Background

EP 233003 A describes a glazing panel carrying a sputter coated optical filter having the structure: glass substrate/SnO₂ base dielectric/first metallic barrier of Al, Ti, Zn, Zr or Ta/Ag/second metallic barrier of Al, Ti, Zn, Zr or Ta/SnO₂ top dielectric. The optical filter is designed to block a significant portion of the incident radiation in the infra red portion of the spectrum whilst allowing passage of a significant portion of the incident radiation in the visible portion of the spectrum. In this way, the filter acts to reduce the heating effect of incident sunlight whilst allowing good visibility through the glazing and is particularly suitable for car windscreens.

In this type of structure, the Ag layer acts to reflect incident infra red radiation and in order to fulfil this role must be maintained as silver metal rather than silver oxide and must not be contaminated by adjacent layers. The dielectric layers which sandwich the Ag layer serve to reduce the reflection of the visible portion of the spectrum which the Ag layer would otherwise provoke. The second barrier serves to prevent oxidation of the Ag layer during sputtering of the overlying SnO₂ dielectric layer in an oxidising atmosphere; this barrier is at least partially oxidised during this process. The main role of the first barrier is to prevent oxidation of the silver layer during heat treatment of the coating (e.g. during bending and/or tempering) of the glazing panel by being oxidised itself rather than allowing passage of oxygen to the Ag layer. This oxidation of the barrier during heat treatment provokes an increase in TL of the glazing panel.

EP 792847A discloses a heat treatable solar control glazing panel which is based on the same principle and has the structure: glass substrate/ZnO dielectric/Zn barrier/Ag/Zn barrier/ZnO dielectric/Zn barrier/Ag/Zn barrier/ZnO dielectric. The Zn barriers positioned below each of the Ag layers are intended to be oxidised completely during heat treatment and serve to protect the Ag layers from oxidation. As well known in the art, the structure of having two, spaced Ag layers rather than a single layer Ag layer increases the selectivity of the filter.

EP 718250A discloses the use of a layer which provides a barrier to oxygen diffusion as at least part of the outermost dielectric layer in this type of filter stack. Such a layer must have a thickness of at least 100 Å and preferably at least 200 Å in order to form an effective barrier and may comprise a silicon compound SiO₂, SiOxCy, SiOxNy, nitrides like Si₃N₄ or AlN, carbides like SiC, TiC, CrC and TaC.

The antireflective layer is a layer composed of at least one member selected from the group consisting of oxides, nitrides and carbides and double compounds thereof.

As the oxide, for example, an oxide of at least one element selected from the group consisting of Zn, Ti, Sn, Si, Al, Ta or Zr may be mentioned. In addition, for example, zinc oxide containing Al, Ga, Si or Sn or indium oxide containing Sn may be mentioned.

As the nitride, a nitride of at least one element selected from the group consisting of Si, Al and B (a nitride (A)) or a mixture (inclusive of a double nitride) of a nitride of Zr or Ti with a nitride (A) may be mentioned.

As the double compound, SiO_(x)C_(y), SiO_(x)N_(y), SiAl_(x)N_(y) or SiAl_(x)O_(y)N_(z) may be mentioned. The antireflective layer may be a single layer or a multiple layer.

Especially, a zinc oxide or a zinc oxide containing at least one element selected from the group consisting of Sn, Al, Cr, Ti, Si, B, Mg, In and Ga is preferable, because it makes it possible to stably form an adjacent infra-red reflecting layer with a high crystallinity. Especially, a zinc oxide containing Al and/or Ti is preferable.

The infra-red reflecting material is a material that has a reflectance higher than the reflectance of sodalime glass in the band of wavelength between 780 nm and 50 μm.

The infra-red reflecting layer is a layer composed of Ag only or a layer comprising Ag as the main component and an additional metal element (such as Pd, Au or Cu). When an additional metal element is contained, the content of the additional metal element is preferably from 0.3 to 10 at %, more preferably from 0.3 to 5 at %, based on the total of Ag and the additional metal element. If the content of an additional metal element is less than 0.3 at %, the effect of stabilizing Ag is small. Also, if the content of an additional metal element exceeds 10 at %, the effect of stabilizing Ag diminishes. Especially, Pd as the additional metal element can immobilize Ag atoms, namely depress the migration of Ag atoms and affords a layer which is excellent in stability and chemical resistance at high temperatures. As the Pd content increases, the rate of film formation tends to decrease, the visible light transmittance tends to lower, and the shielding selectivity between visible rays and near infrared rays tends to become poor. Therefore, the Pd content (Pd/Ag) is preferred to be at most 5.0 at %, especially from 0.3 to 2.0 at %, more preferably from 0.3 to 1.0 at %.

When the glass laminate of the present invention comprises more than one infra-red reflecting layer, each infra-red layer may have the same composition or a different composition. The infra-red reflecting layer may be a multiple layer comprising at least two laminated films, for example, a multiple layer composed of Ag and Pd.

In a glazing panel having a three layer type laminated coating, the thickness of the base antireflective layer, the infra-red layer and the top antireflective layer layer are preferably from 15 to 45 nm, from 9 to 16 nm (especially from 9 to 12 nm) and from 30 to 45 nm, respectively. A glazing panel comprising a colorless soda lime glass substrate of 2 mm thick and a three layer type laminated coating formed on the substrate has such representative optical properties as a luminous transmittance (TL) of about from 75 to 85% and an energetic transmittance (TE) of about from 50 to 70% after heat treatment.

In a glazing panel having a five layer type laminated coating, the thicknesses of the base antireflective layer, the infra-red layer the central antireflective layer, the infra-red layer and the top antireflective layer layer are preferably from 16 to 50 nm (especially from 20 to 45 nm), from 6.5 to 16 nm (especially from 6.5 to 12.5 nm), from 40 to 100 nm (especially from 45 to 90 nm), from 6.5 to 16 nm (especially from 6.5 to 12.5 nm) and from 16 to 50 nm (especially from 20 to 45 nm), respectively. A glazing panel comprising a colorless soda lime glass substrate of 2 mm thick and a five layer type laminated coating formed on the substrate has such representative optical properties as a luminous transmittance (TL) of about from 70 to 80% and an energetic transmittance (TE) of about from 40 to 50% after heat treatment.

DETAILED DESCRIPTION OF THE INVENTION

The term “heat treatable glazing panel” as used herein means that the glazing panel carrying the coating stack is adapted to undergo a bending and/or thermal tempering and/or thermal hardening operation and/or other heat treatment process without the haze of the so treated glazing panel exceeding 0.5, and preferably without the haze exceeding 0.3. The term “substantially haze free heat treated glazing panel” as used herein means a glazing panel carrying a coating stack which has been bent and/or thermally tempered and/or thermally hardened and has a haze that does not exceed 0.5 and which preferably does not exceed 0.3. In the present invention, a glazing panel can be subjected to heat treatment for 1) bending, 2) tempering, 3) sintering of colored ceramic print or silver bus bar print, 4) vacuum sealing of vacuum double glazing and 5) calcination of a wet-coated low reflective coating or antiglare coating. For example, it is heated to a temperature of from 570 to 700° C. in the atmosphere for 1) bending or 2) tempering. The bending and/or thermal tempering and/or thermal hardening operation may be carried out at a temperature of at least, 600° C. for at least 10 minutes, 12 minutes, or 15 minutes, at least 620° C. for at least 10 minutes, 12 minutes, or 15 minutes, or at least 640° C. for at least 10 minutes, 12 minutes, or 15 minutes.

Any suitable method or combination of methods may be used to deposit the coating layers. For example, evaporation (thermal or electron beam), liquid pyrolysis, chemical vapour deposition, vacuum deposition and sputtering, particularly magnetron sputtering, the latter being particularly preferred. Different layers of the coating stack may be deposited using different techniques.

The nitride of aluminium may be pure AlN, substantially pure AlN, AlN containing impurities or AlN containing one or more dopants, for example, chromium and/or silicon and/or titanium, which may improve chemical durability of the material. The nitride of aluminium may contain about 97% pure AlN by weight. Alternatively, it may contain an oxynitride, a carbonitride or an oxycarbonitride. The nitride of aluminium may be deposited by sputtering a target in a nitrogen atmosphere. Alternatively, it may be deposited by sputtering a target in an atmosphere which is a mixture of argon and nitrogen.

The target may be 6061 alloy, 6066 alloy, 4032 alloy, etc.

A nitride of aluminium in the base antireflective layer is believed effective in blocking not only oxygen but also sodium ions and other ions that can diffuse from the glass into the coating stack and cause a deterioration of optical and electrical properties, particularly if the glazing panel is subjected to heat treatment.

SiO₂ and Al₂O₃ are known to be effective barriers to diffusion of sodium ions in sputtered coating stacks. In addition to being easier, quicker and more cost effective to deposit by sputtering, it is believed that a nitride of aluminium as part of the base dielectric layer provides an effective barrier to both sodium ions and oxygen diffusion. Furthermore, it is believed that a nitride of aluminium may provide an effective diffusion barrier at smaller geometrical thicknesses than that required using known materials. For example, good thermal resistance with respect to ion and oxygen diffusion from the glass substrate may be conferred on the coating stack by arranging a nitride of aluminium having a geometrical thickness of greater than 40 Å, for example, about 50 Å as at least part of the base antireflective layer particularly if the coating stack also includes a barrier layer, for example a metal or sub-oxide barrier layer, underlying the infrared reflecting layer. In the absence of such a barrier layer underlying the infra-red reflecting layer, good thermal resistance with respect to ion and oxygen diffusion from the glass substrate may be conferred on the coating stack by arranging a nitride of aluminium having a geometrical thickness of greater than 50 Å, preferably greater than 80 Å or 90 Å, for example, about 100 Å as at least part of the base antireflective layer. A layer of a nitride of aluminium may confer advantageous properties even if it is less than 195 Å thick.

The coating stack may comprise a barrier layer overlying the infra red reflecting layer and/or a barrier layer underlying the infra red reflecting layer. Such barriers may contain one or more metals and may be deposited, for example, as metal oxides, as metal sub-oxides or as metals.

Further, in the invention, when a layer composed of an oxide or a double compound containing an oxide such as an oxynitride is formed as an antireflective layer by reactive sputtering in an atmosphere containing an oxidative gas, formation of such antireflective layer directly on the infra-red reflecting layer can fail to give a glazing panel having desired optical and electrical properties because of oxidation of the infra-red reflecting layer Therefore, it is preferred to form a metal or nitride barrier layer. Such a barrier layer usually stays in a partly oxidized state, and during heat treatment, oxidizes into a transparent oxide having a higher visible light transmittance.

As the barrier layer, a metal of at least one element selected from the group consisting of Ti, Zn, Al—Zn, Ti—Zn, SUS, Zr, Ta, NiCr, Ni, Ni—Ti, a nitride of at least one element selected from the group consisting of Ti, Zn, Al—Zn, Ti—Zn, SUS, Zr, Ta, NiCr, Ni, Ni—Ti, and a sub-oxide (i.e. partially oxized) of at least one element selected from the group consisting of Ti, Zn, Al—Zn, Ti—Zn, SUS, Zr, Ta, NiCr, Ni, Ni—Ti is preferable. The thickness of a barrier layer is preferably from 1 to 5 nm. A barrier layer thinner than 1 nm does not work well, while a barrier layer thicker than 5 nm can lower the visible light transmittance of the glass laminate or cause other problems.

When an oxide layer, for example, composed of zinc oxide containing Al is formed directly on the infra-red reflecting layer as the antireflective layer, an Al—Zn alloy barrier layer having the same metal ratio can strengthen the adhesion between the infra-red reflecting layer and the antireflective layer and thus is effective in improving durability of the layers of the multilayer structure. An Al—Zn alloy barrier layer is also preferable in view of the crystallinity of Ag in the infra-red reflecting layer and the heat resistance. A barrier layer may be formed under the infra-red reflecting layer, too.

The ability to block ion and oxygen diffusion from the glass substrate with a relatively thin layer provides great flexibility in the materials and thickness that may be used for the other layers in the coating stack.

Providing a layer of a metal oxide between the nitride of aluminium and the infra-red reflecting material (particularly when this is silver or a silver alloy) may combine the thermal stability properties of the nitride of aluminium with an interposed material which favours crystallisation of the infra-red reflecting material so as to balance the infra red reflecting properties with the haze of the coating stack, particularly when it is subjected to heat treatment. One preferred such oxide is a mixed oxide of zinc and aluminium, preferably with a Al/Zn atomic ratio of about 0.1-0.2, especially 0.1-0.15. One possible explanation for this may be that the presence of the Al in the zinc oxide structure may reduce the crystal grain growth in the mixed oxide layer.

The effectiveness of a relatively thin layer of the nitride of aluminium in conferring thermal stability allows use of a relatively thick layer of such an oxide.

Both Si₃N₄ and AlN take longer to deposit by common sputtering techniques than oxides traditionally used in such coatings e.g. ZnO, SnO₂. The ability to provide good thermal stability with a relatively thin layer of a nitride of aluminium thus alleviates the deposition of such a layer as a limiting factor in a deposition process.

A nitride of aluminium is also more cost effective to deposit by sputtering than, for example, Si₃N₄ and does not require the doping or control precautions required for depositing Si₃N₄.

The optical thickness of the antireflective layers and particularly that of the top antireflective layer is critical in determining the colour of the glazing panel. If a portion of an antireflective layer is oxidised, for example during heat treatment of the glazing panel then, particularly with Si₃N₄ (refractive index about 2) the optical thickness can be modified as Si₃N₄ may be oxidised to SiO₂ (refractive index about 1.45). Where the antireflective layer comprises a nitride of aluminium having a refractive index of about 2.0, oxidation of a part of this to Al₂O₃ (refractive index about 1.7) will have negligible effect upon the optical thickness of the layer.

The ability to use a layer of a nitride of aluminium which is less than 100 Å in thickness to provide an effective thermal barrier provides significant flexibility in the choice of the overall structure of the top antireflective layer. The layer comprising a nitride of aluminium may be about 85 Å in thickness; this provides a compromise between good thermal resistance and thickness. The layer comprising a nitride of aluminium may have a geometrical thickness of greater than or equal to about 50 Å, 60 Å or 80 Å; its thickness may be less than or equal to about 85 Å, 90 Å or 95 Å.

Heat treatment may provoke an increase in the TL of the glazing panel. Such an increase in TL may be advantageous in ensuring that TL is sufficiently high for the glazing panel to be used in a vehicle windscreen. TL may increase in absolute terms during heat treatment by, for example, greater than about 2.5%, greater than about 3%, greater than about 5%, greater than about 8% or greater than about 10%.

Examples of the present invention will now be described with reference to FIG. 1 which is a cross-section through a glazing panel prior to a bending and tempering operation (for ease of representation, the relative thicknesses of the glazing panel and coating layers are not shown to scale).

EXAMPLE 1

FIG. 1 shows a double Ag layer, heat treatable, coating layer deposited on a glass substrate by magnetron sputtering and having the following sequential structure:

Reference Geometrical number thickness Atomic ratios Glass substrate 10 2 mm Base dielectric 11 comprising: AlN 12  60 Å ZnAlOx 13 250 Å Al/Zn = 0.1 ZnAlOy underlying barrier 14  10 Å Al/Zn = 0.1 Ag 15 100 Å ZnAlOy overlying barrier 16  12 Å Al/Zn = 0.1 Central dielectric ZnAlOx 17 750 Å Al/Zn = 0.1 comprising ZnAlOy underlying barrier 18  7 Å Al/Zn = 0.1 Ag 19 100 Å ZnAlOy overlying barrier 20  17 Å Al/Zn = 0.1 Top dielectric comprising: ZnAlOx 22 185 Å Al/Zn = 0.1 AlN 23  85 Å

in which ZnAlOx is a mixed oxide containing Zn and Al deposited in this example by reactively sputtering a target which is an alloy or mixture of Zn and Al in the presence of oxygen. The ZnAlOy barriers are similarly deposited by sputtering a target which is an alloy or mixture of Zn and Al in an argon rich oxygen containing atmosphere to deposit a barrier that is not fully oxidised.

Alternatively, the mixed oxide layer ZnAlOx may be formed by sputtering a target which is a mixture of zinc oxide and an oxide of Al, particularly in an argon gas or argon rich oxygen containing atmosphere.

Where the barrier layers comprise the same materials as the mixed oxide layer, particularly the adjacent mixed oxide layer, this may facilitate management of targets and control of deposition conditions and may provide good adhesion between the layers and thus good mechanical durability of the coating stack.

The oxidation state in each of the base, central and top ZnAlOx dielectric layers need not necessarily be the same. Similarly, the oxidation state in each of the ZnAlOy barriers need not be the same. Equally, the Al/Zn ratio need not be the same for all of the layers; for example, the barrier layers may have a different Al/Zn ratio to the antireflective dielectric layers and the antireflective dielectric layers may have different Al/Zn ratios from each other.

Each overlying barrier protects its underlying silver layer from oxidation during sputter deposition of its overlying ZnAlOx oxide layer. Whilst further oxidation of these barrier layers may occur during deposition of their overlying oxide layers a portion of these barriers preferably remains in the form of an oxide that is not fully oxidised to provide a barrier for subsequent heat treatment of the glazing panel.

This particular glazing panel is intended for incorporation in a laminated vehicle windscreen and displays the following properties:

Prior to heat Following heat treatment see Note 1 treatment see Note 2 Property below below TL(Illuminant A) 63% 76% TE (System Moon 2) 38% 42% haze 0.1 0.25 a* −20 (coated side)  −6 (external) b*  +3 (coated side) −12 (external) RE (System Moon 2) 31% (coated side) 33% (external) Note 1: Measured for monolithic glazing panel with coating prior to heat treatment Note 2: Measured following heat treatment at 650° C., for 10 minutes followed by bending and tempering, and lamination with clear 2 mm glass sheet and 0.76 mm clear pvb

Heat treatment preferably causes substantially complete oxidation of all of the barrier layers such that the structure of the coating stack after heat treatment is:

Reference Geometrical number thickness Atomic ratios Glass substrate 10 2 mm Base dielectric comprising: 11 AlN (partially oxidised) 12  60 Å ZnAlOx 13 250 Å Al/Zn = 0.1 ZnAlOx (oxidised underlying 14 10 Å-16 Å Al/Zn = 0.1 barrier) Ag 15 100 Å ZnAlOx (oxidised overlying 16  12 Å-20 Å Al/Zn = 0.1 barrier) Central dielectric 17 750 Å Al/Zn = 0.1 comprising ZnAlOx ZnAlOx (oxidised underlying 18  7 Å-12 Å Al/Zn = 0.1 barrier) Ag 19 100 Å ZnAlOx (oxidised overlying 20  17 Å-28 Å Al/Zn = 0.1 barrier) Top dielectric comprising: ZnAlOx 22 185 Å Al/Zn = 0.1 AlN (partially oxidised) 23  85 Å

The AlN (partially oxidised) layers may comprise a mixture of AlN and Al₂O₃, the AlN being partially oxidised during the heat treatment process. The barrier layers are not necessarily completely oxidised and their thickness will depend to a certain extent upon their degree of oxidation.

EXAMPLE 2

Example 2 is similar to Example 1, save that the underlying barriers of the coating stack were omitted. The coating stacks and properties of the Example are set out below:

Reference Geometrical number thickness Atomic ratios Glass substrate 10 2 mm Base dielectric 11 comprising: AlN 12 100 Å ZnAlOx 13 200 Å Al/Zn = 0.1 Ag 15 100 Å ZnAl overlying barrier 16  10 Å Al/Zn = 0.1 Central dielectric 17 750 Å Al/Zn = 0.1 comprising ZnAlOx Ag 19 100 Å ZnAl overlying barrier 20  15 Å Al/Zn = 0.1 Top dielectric comprising: ZnAlOx 22 185 Å Al/Zn = 0.1 AlN 23  85 Å

in which ZnAlOx is a mixed oxide containing Zn and Al deposited in this example by reactively sputtering a target which is an alloy or mixture of Zn and Al in the presence of oxygen. The ZnAl barriers are similarly deposited by sputtering a target which is an alloy or mixture of Zn and Al in a substantially inert, oxygen free atmosphere.

At least a portion of the overlying barriers 16, 20 is oxidised during deposition of their overlying oxide layers. Nevertheless, a portion of these barriers preferably remains in metallic form, or at least in the form of an oxide that is not fully oxidised to provide a barrier for subsequent heat treatment of the glazing panel.

This particular glazing panel is intended for incorporation in a laminated vehicle windscreen and displays the following properties:

Prior to heat Following heat treatment see Note 1 treatment see Note 2 Property below below TL (Illuminant A) 70% 77% TE (System Moon 2) 41% 43% haze 0.1 0.2 a* −17 (coated side) −5 (external) b*  +8 (coated side) −9 (external) RE (System Moon 2) 33% (coated side) 34% (external) Note 1: Measured for monolithic glazing panel with coating prior to heat treatment Note 2: Measured following heat treatment at 625° C. for 14 minutes followed by bending and tempering, and lamination with clear 2 mm glass sheet and 0.76 mm clear pvb

Heat treatment preferably causes substantially complete oxidation of all of the barrier layers such that the structure of the coating stack after heat treatment is:

Coating Stack Following Heat Treatment

Reference Geometrical number thickness Atomic ratios Glass substrate 10 2 mm Base dielectric comprising: 11 AlN (partially oxidised) 12 100 Å ZnAlOx 13 200 Å Al/Zn = 0.1 Ag 15 100 Å ZnAlOx (oxidised overlying 16  12-20 Å Al/Zn = 0.1 barrier) Central dielectric 17 750 Å Al/Zn = 0.1 comprising ZnAlOx Ag 19 100 Å ZnAlOx (oxidised overlying 20  17-30 Å Al/Zn = 0.1 barrier) Top dielectric comprising: ZnAlOx 22 185 Å Al/Zn = 0.1 AlN (partially oxidised) 23  85 Å

Additional layers may be introduced above, below or between the film stacking arrangement if desired without departing from the invention.

In addition to the advantageous optical properties that may be obtained, each of the examples provides a coating layer which may be electrically heated, for example, in an electrically heated car windscreen to provide a de-misting and/or de-frosting function with the addition of suitably placed electrical connectors.

The colour co-ordinates of the examples are particularly suited to car windscreens as they give a neutral or slightly blue or slightly green appearance in reflection when the windscreen is mounted at an angle in the car body. For other applications, for example architectural applications, the colour in reflection may be adjusted as is known in the art by adjusting the thicknesses of the dielectric layers and/or silver layer(s).

EXAMPLE 3

Example 3 is similar to Example 2. The coating stacks and properties of the Example are set out below:

Reference Geometrical number thickness Atomic ratios Glass substrate 10 2 mm Base dielectric 11 comprising: AlNx 12 110 Å ZnAlOx 13 240 Å Al/Zn = 0.14 Ag 15 100 Å ZnAl overlying barrier 16  12 Å Al/Zn = 0.14 Central dielectric 17 750 Å Al/Zn = 0.14 comprising ZnAlOx Ag 19 100 Å ZnAl overlying barrier 20  18 Å Al/Zn = 0.14 Top dielectric comprising: ZnAlOx 22 180 Å Al/Zn = 0.14 AlNx 23  85 Å

At least a portion of the overlying barriers 16, 20 is oxidised during deposition of their overlying oxide layers. Nevertheless, a portion of these barriers preferably remains in metallic form, or at least in the form of an oxide that is not fully oxidised to provide a barrier for subsequent heat treatment of the glazing panel.

This particular glazing panel is intended for incorporation in a laminated vehicle windscreen and displays the following properties:

Prior to heat Following heat treatment see Note 1 treatment see Note 2 Property below below TL (Illuminant A) — 76% TE (System Moon 2) — 43% haze — 0.23 a* −10 (coated side) — b* — — RE (System Moon 2) — 32% (external) Note 1: Measured for monolithic glazing panel with coating prior to heat treatment Note 2: Measured following heat treatment at 645° C. for 14 minutes with bending and tempering, and lamination with clear 2 mm glass sheet and 0.76 mm clear pvb

EXAMPLES 4

Example 4 is similar to Example 2. The coating stacks and properties of the Example are set out below:

Reference Geometrical number thickness Atomic ratios Glass substrate 10 2 mm Base dielectric 11 comprising: AlNx 12 100 Å ZnAlOx 13 220 Å Al/Zn = 0.14 Ag 15 100 Å ZnAl overlying barrier 16  12 Å Al/Zn = 0.14 Central dielectric 17 800 Å Al/Zn = 0.14 comprising ZnAlOx Ag 19 100 Å ZnAl overlying barrier 20  18 Å Al/Zn = 0.14 Top dielectric comprising: ZnAlOx 22 180 Å Al/Zn = 0.14 AlNx 23  85 Å

At least a portion of the overlying barriers 16, 20 is oxidised during deposition of their overlying oxide layers. Nevertheless, a portion of these barriers preferably remains in metallic form, or at least in the form of an oxide that is not fully oxidised to provide a barrier for subsequent heat treatment of the glazing panel.

This particular glazing panel is intended for incorporation in a laminated vehicle windscreen and displays the following properties:

Prior to heat Following heat treatment see Note 1 treatment see Note 2 Property below below TL (Illuminant A) — 75.5% TE (System Moon 2) — 43.4% haze — 0.21 a* — — b* — — RE (System Moon 2) — 31.5% (external) Note 1: Measured for monolithic glazing panel with coating prior to heat treatment Note 2: Measured following heat treatment at 645° C. for 14 minutes with bending and tempering, and lamination with clear 2 mm glass sheet and 0.76 mm clear pvb

EXAMPLES 5

Example 5 is similar to Example 2. The coating stacks and properties of the Example are set out below:

Reference Geometrical number thickness Atomic ratios Glass substrate 10 2 mm Base dielectric 11 Comprising: AlNx 12 100Å ZnAlOx 13 220Å Al/Zn = 0.05 Ag—Pd 15 100Å Pd/Ag = 0.005 ZnAl overlying barrier 16  12Å Al/Zn = 0.05 Central dielectric Comprising ZnAlOx 17 800Å Al/Zn = 0.05 Ag—Pd 19 100Å Pd/Ag = 0.005 ZnAl overlying barrier 20  18Å Al/Zn = 0.05 Top dielectric comprising: ZnAlOx 22 180Å Al/Zn = 0.05 AlNx 23  85Å

At least a portion of the overlying barriers 16, 20 is oxidised during deposition of their overlying oxide layers. Nevertheless, a portion of these barriers preferably remains in metallic form, or at least in the form of an oxide that is not fully oxidised to provide a barrier for subsequent heat treatment of the glazing panel.

This particular glazing panel is intended for incorporation in a laminated vehicle windscreen and displays the following properties:

Prior to heat Following heat treatment see Note 1 treatment see Note 2 Property below below TL (Illuminant A) — 75.2% TE (System Moon 2) — 42.9% haze — 0.24 a* — — b* — — RE (System Moon 2) — 31.4% (external) Note 1: Measured for monolithic glazing panel with coating prior to heat treatment Note 2: Measured following heat treatment at 645° C. for 14 minutes with bending and tempering, and lamination with clear 2 mm glass sheet and 0.76 mm clear pvb

Glossary

Unless otherwise indicated by the context, the terms listed below have the following meanings in this specification:

a* colour co-ordinate measured on the CIELab scale at normal incidence Ag silver Al aluminium Al2O3 aluminium oxide AlN aluminium nitride b* colour co-ordinate measured on the CIELab scale at normal incidence Bi bismuth Cr chromium haze the percentage of transmitted light which in passing through the specimen deviates from the incident beam by forward scattering, as measured in accordance with the ASTM Designation D 1003-61 (Reapproved 1988). Hf hafnium infra red a material that has a reflectance higher than reflecting the reflectance of sodalime glass in the band material of wavelenghts between 780 nm and 50 microns Na sodium Nb niobium NiCr an alloy or mixture comprising nickel and chromium NiTi an alloy or mixture comprising nickel and titanium RE energetic the solar flux (luminous and non-luminous) reflection reflected from a substrate as a percentage of the incident solar flux Sb antimony selectivity the ratio of the luminous transmittance to the solar factor i.e. TL/TE SiO2 silicon oxide Si3N4 silicon nitride SnO2 tin oxide Ta tantalum TE energetic the solar flux (luminous and non-luminous) transmittance transmitted through a substrate as a percentage of the incident solar flux Ti titanium TL luminous the luminous flux transmitted through a transmittance substrate as a percentage of the incident luminous flux Zn zinc ZnAl an alloy or mixture comprising zinc and aluminium ZnAlOx a mixed oxide containing zinc and aluminium ZnAlOy a partially oxidised mixture comprising zinc and aluminium ZnO zinc oxide ZnTi an alloy or mixture comprising zinc and titanium ZnTiOx a mixed oxide containing zinc and titanium ZnTiOy a partially oxidised mixture comprising zinc and titanium Zr zirconium 

What is claimed is:
 1. A heat treatable glazing panel carrying a coating stack comprising in sequence at least: a glass substrate a base antireflective layer an infra-red reflecting layer, and a top antireflective layer characterised in that the base antireflective layer comprises at least one layer comprising a nitride of aluminium; wherein said infra-red reflecting layer comprises Ag as the main component and Pd in an amount of from 0.3 to 5.0 at % to Ag.
 2. A heat treatable glazing panel in accordance with claim 1 comprising in sequence at least: a glass substrate a base antireflective layer an infra-red reflecting layer a central antireflective layer an infra-red reflecting layer a top antireflective layer characterised in that the base antireflective layer comprises at least one layer comprising a nitride of aluminium; wherein each of said infra-red reflecting layers comprise Ag as the main component and Pd in an amount of from 0.3 to 5.0 at % to Ag.
 3. A heat treatable glazing panel carrying a solar control coating stack comprising in sequence at least: a glass substrate a base antireflective layer an infra-red reflecting layer, and a top antireflective layer characterised in that the top antireflective layer comprises at least one layer comprising a nitride of aluminium having a geometrical thickness of less than 100 Å; wherein the base antireflective layer comprises a first layer adjacent to the substrate comprising a nitride of aluminium and an overlying layer comprising a mixed oxide of zinc and aluminium having an atomic ratio Al/Zn of greater than or equal to 0.05 and less than or equal to 0.25.
 4. A heat treatable glazing panel in accordance with claim 1, in which heat treatment of the heat treatable glazing panel to form the substantially haze free heat treated glazing panel provokes an increase of the value of TL of the glazing panel of at least 2.5%.
 5. A method of manufacturing a glazing panel having a haze of less than about 0.5 comprising the step of manufacturing a glazing panel in accordance with claim 1, to a heat treatment process at least 570° C.
 6. A heat treatable glazing panel in accordance with claim 1, wherein said Pd is present in said infra-red reflecting layer in an amount of from 0.3 to 2.0 at %.
 7. A heat treatable glazing panel in accordance with claim 1, wherein said Pd is present in said infra-red reflecting layer in an amount of from 0.3 to 1.0 at %.
 8. A heat treatable glazing panel in accordance with claim 3, wherein said Al/Zn ratio is from 0.05-0.20.
 9. A heat treatable glazing panel in accordance with claim 3, wherein said Al/Zn ratio is from 0.05-0.15.
 10. A heat treatable glazing panel in accordance with claim 3, further comprising an Al—Zn alloy barrier layer overlying the infra-red reflecting layer, and wherein said Al/Zn ratio is from 0.05-0.25.
 11. A heat treatable glazing panel in accordance with claim 10, wherein said Al/Zn ratio is from 0.05-0.20.
 12. A heat treatable glazing panel in accordance with claim 10, wherein said Al/Zn ratio is from 0.05-0.15.
 13. A heat treatable glazing panel carrying a coating stack comprising in sequence at least: a glass substrate a base antireflective layer an infra-red reflecting layer, and a top antireflective layer characterised in that the base antireflective layer comprises at least one layer comprising a nitride of aluminium, which is adjacent the glass substrate; wherein said infra-red reflecting layer comprises Ag as the main component and Pd in an amount of from 0.3 to 5.0 at % to Ag.
 14. A substantially haze free glazing panel obtained by heat treating the heat treatable glazing panel of claim
 1. 15. A substantially haze free glazing panel obtained by heat treating the heat treatable glazing panel of claim
 2. 16. A substantially haze free glazing panel obtained by heat treating the heat treatable glazing panel of claim
 3. 17. A substantially haze free glazing panel obtained by heat treating the heat treatable glazing panel of claim
 4. 18. A substantially haze free glazing panel obtained by heat treating the heat treatable glazing panel of claim
 6. 19. A substantially haze free glazing panel obtained by heat treating the heat treatable glazing panel of claim
 7. 20. A substantially haze free glazing panel obtained by heat treating the heat treatable glazing panel of claim
 8. 21. A substantially haze free glazing panel obtained by heat treating the heat treatable glazing panel of claim
 9. 22. A substantially haze free glazing panel obtained by heat treating the heat treatable glazing panel of claim
 10. 23. A substantially haze free glazing panel obtained by heat treating the heat treatable glazing panel of claim
 11. 24. A substantially haze free glazing panel obtained by heat treating the heat treatable glazing panel of claim
 12. 25. A substantially haze free glazing panel obtained by heat treating the heat treatable glazing panel of claim
 13. 